The present invention relates to stringed musical instruments, such as, acoustic guitars, and more particularly, the present invention relates to a novel acoustic guitar assembly which includes a soundboard made of composite materials.
A typical acoustic guitar has a hollow body connected to a neck. The hollow body has a soundboard with a soundhole, a backboard spaced from the soundboard, and a shaped sidewall which extends between the soundboard and backboard. Typically, these components are constructed of choice pieces of wood.
Prior art designs have attempted to improve upon the strength and durability of acoustic guitars without adversely affecting the playing qualities of the guitar. For example, U.S. Pat. No. 5,461,958 which issued to Dresdner et al. and which is assigned to C.F. Martin and Company, Inc., the assignee of the present application, discloses an acoustic guitar assembly having a wooden soundboard with an improved soundboard bracing structure and an improved neck to body joint.
Acoustic guitar bodies have also been manufactured from high pressure laminate materials. For example, U.S. Pat. No. 5,406,874 issued to Witchel and assigned to C.F. Martin and Company, Inc. discloses a sidewall, soundboard and baseboard of a hollow body of an acoustic guitar constructed of sheets of synthetic resin laminates, such as, melamine impregnated resins impressed over phenolic kraft layers.
U.S. Pat. Nos. 5,952,592, 6,034,309 and 6,420,638 issued to Teel and assigned to C.F. Martin and Company, Inc. provide additional examples of an acoustic guitar body made of high pressure laminate materials. The ""592 patent discloses a unique bracing pattern specifically for use on the underside of a soundboard made of high pressure laminate materials. The ""309 patent discloses a method of manufacturing a guitar body made of high pressure laminate materials, and the ""638 patent discloses a guitar neck made of plywood impregnated with a phenolic resin and a fingerboard and/or guitar bridge made of a high pressure laminate material. In addition, co-pending U.S. patent application Ser. No. 09/862,273 filed on May 22, 2001 discloses a soundboard and/or headplate made of metal, such as aluminum. The above referenced acoustic guitars assembled from unconventional materials provide an economic alternative for purchasers of high quality acoustic guitars, and due to dwindling wood resources, provide an ecologically-friendly alternative to traditional solid and laminated tonewoods.
Another material utilized to construct components of acoustic guitars is graphite, or carbon, fibers. For example, U.S. Pat. No. 5,333,527 issued to Janes et al. discloses an acoustic guitar constructed with a compression molded composite soundboard made of multiple layers of epoxy impregnated graphite fibers formed of about 33% by volume of resin and about 67% by volume of graphite fiber. The uppermost and lowermost layers of the composite soundboard are a woven graphite fiber fabric, and the inner layers are laminates in which the graphite fibers are unidirectionally-oriented. For instance, the direction of the fibers in some of the laminates are oriented such that they extend parallel to the strings of the instrument, while the direction of fibers in other of the laminates extend perpendicular to the strings of the instrument.
Other stringed musical instruments have also been constructed from graphite, or carbon, fibers and are disclosed, for example, in U.S. Pat. Nos: 4,408,516 issued to John; 4,873,907 and 4,969,381 issued to Decker, Jr. et al.; 6,107,552 issued to Coomar et al.; and 6,294,718 issued to Saunders, Jr. et al. The John patent discloses a violin made from a plurality of sheets of unidirectional graphite fibers impregnated with an epoxy resin in which the resin forms 40% by volume and fibers form 60% by volume. The direction of the fibers of some of the layers are oriented parallel to the strings of the instrument while the direction of the fibers in other of the layers are oriented perpendicular to the strings and at a 45xc2x0 angle relative to the strings. The Decker patents disclose an acoustic guitar having a composite soundboard made of a lay-up of woven polymer fabric, preferably an aramid fabric, and a layer of unidirectional graphite fibers followed by a layer of decorative fabric, such as silk, which are all embedded in a resin matrix. The Coomar and Saunders patents disclose soundboards including a wooden or foam core material sandwiched between layers of a graphite sheet material embedded in an epoxy resin.
Also see U.S. Pat. No. 4,429,608 issued to Kaman et al. which discloses a one layer molded plastic soundboard made of 40% glass fibers and 60% resin with the fibers being randomly oriented, and U.S. Pat. No. 4,836,076 issued to Bernier which discloses a molded violin having a soundboard made of resin, fiberglass and/or fiber plastic.
Although the above-mentioned stringed musical instruments accomplish their intended purposes, there is a need for a high quality, durable acoustic guitar which is constructed from relatively inexpensive unconventional materials, particularly laminate materials, which provide both a unique decorative appearance and superior acoustic qualities. In particular, the hollow body of the acoustic guitar should have a composite graphite soundboard and a high pressure laminate sidewall and backboard. In addition, the underside of the soundboard should include bracing that provides the acoustic guitar with the necessary durability as well as with desired tonal and playing qualities.
With the foregoing in mind, a primary object of the present invention is to provide a high quality acoustic guitar which can be manufactured economically relative to traditional all wooden acoustic guitar models.
Another object of the present invention is to provide an acoustic guitar having a uniquely braced graphite soundboard which does not adversely affect the tonal qualities of the guitar.
More specifically, the present invention provides an acoustic guitar having a hollow body and an elongate neck extending from said hollow body. The hollow body has a composite soundboard with a substantially planar underside and a soundhole. The composite soundboard is constructed from laminate sheet material made of multiple layers of epoxy impregnated graphite fibers. Preferably, the graphite fibers within each layer are unidirectionally-oriented within each layer such that at least some of the layers of the laminate sheet material extend parallel to the strings of the acoustic guitar.
The composite soundboard of the present invention preferably has bracing made of spruce adhesively secured to, and depending from, the underside of the composite soundboard. The bracing includes an X-shaped cross brace and an A-frame brace. The cross brace has four legs defining four quadrants on the soundboard, and a pair of the legs define a first quadrant in which the soundhole is located and the other pair of legs define an opposite quadrant on the soundboard remote from the guitar neck. The A-frame brace is located in the first quadrant between the soundhole and the guitar neck and cooperates with the cross brace to completely surround and reinforce the soundhole. The bracing is preferably secured to the underside of the soundboard with an acrylic adhesive that cures at room temperature or an epoxy adhesive that cures at room temperature.
The hollow body of the acoustic guitar has a backboard spaced from the graphite soundboard and a sidewall extending between and connecting the graphite soundboard and backboard. The backboard and sidewall are each constructed of a pre-finished high pressure laminate material. Preferably, the pre-finished laminate material utilized to make the sidewall and backboard is sheets of synthetic resin laminates, such as, melamine impregnated resins impressed over phenolic kraft layers.